The study salt and drought tolerance of Sinorhizobium bacteria to the adaptation to alkaline condition

Salinity, alkalinity and drought stress are the major abiotic stresses hindering the productivity of alfalfa (Medicago Sativa) in arid and semi-arid regions. Therefore an ecological survey was conducted to characterize 600 Sinirhizobium strains of diverse geographical origin, isolated from the root nodules of alfalfa (Medicago Sativa). Rhizobial isolates were studied under free living conditions. Shinorhizobium sp. Tolerated yeast extract mannitol broth (YEB) containing 0, 1%, 2.5% and 4.5% salt (NaCl, wt/vol) for up 18 h of incubation at 300C. Growth of Shinorhizobium sp. at water potential 0, -1, -2 and -3.5 MPa (with PEG6000, wt/vol) for up 18 h of incubation at 300C was identical. The results showed that salinity and drought tolerance among isolates was significantly different. All isolates were grouped in two clusters: sensitive and tolerant based on their growth rate in YEB media containing different concentrations of NaCl and PEG . To obtain strains resistant to alkaline conditions (high pH range between 7-9) the medium was buffered with AMPD buffer, while for the low pH range between 4 and 5 it was buffered with 25 mM HOMOPIPES A positive correlation was found between the salt tolerance and the adaptation to alkaline pH